In terms of player transfer fees, this is entirely up to the club. Sometimes you see an ordinary being priced with no sense of value, such as Mudryk or even Enzo Fernandes, but I must emphasize that you can still get an A+ or S-tier player for 100 million euros.
It can be different if this is related to a player on Tier SS.
Again, Osimhen's price was set by Napoli, and I'm not sure how Napoli valued their players, but 130 millions for Osimhen is ridiculous.
It makes sense if his price is around 80 millions.
Osimhen is significantly worse than Mbappe and Haaland; However, anything over a hundred million euros is prohibitively expensive. Finally, PSG has dropped their interest in Osimhen.
For now it seems that we are starting to find it difficult to find a player or striker who is included in the A+ because indeed the club that owns them has fenced them with a long contract and also a high release clause, so it is indeed very difficult to get him, PSG and several other teams are rumored to be very interested in bringing Osimhen to their team and even Osimhen has also confirmed if he wants to go to another better team at the moment, But Osimhen mistake when he extended his contract at the end of last season so that indeed Napoli set a very high release clause on Osimhen at the moment, in my opinion, after several teams withdrew from the competition for Osimhen at the moment, it seems that Osimhen inevitably has to stay at Napoli even though indeed his position as the main striker may be threatened after Conte takes over the team.
Osimhen performance in the last two seasons is indeed quite good and even he is very consistent in scoring goals, but as you say, of course Osimhen is still not worthy of being valued so expensive by Napoli at the moment, rather than buying Osimhen who does have a very high price, of course other teams currently prefer to bring in other strikers who indeed with 100 million euros they can get 2-3 new players later.